This disclosure relates to gas flow measurement equipment and, in particular, to equipment, systems, and methods designed to improve the accuracy of gas flow measurement in custody transfer transactions along a gas pipeline. Because of the tremendous volume of gas being transferred between pipeline companies, small measurement errors can have very large financial effects.
To measure gas flow through a pipeline, ultrasonic gas flow meters are placed along a section of pipe. A front end treatment or elbow diverts the main pipeline flow toward the flow meter and reduces swirl using a flow conditioner placed 10 pipeline diameters ahead of the flow meter. The conditioner provides a bullet-nosed gas flow profile into the meter. A backend treatment or elbow located at least 5 pipeline diameters after the meter brings the now-measured gas flow back in line with the main pipeline (see FIG. 1). The backend elbow, along with a blind flange located opposite the main pipeline, helps attenuate ultrasonic waves generated by downstream equipment such as a control valve and prevents those waves from traveling back to the flow meter and interfering with flow measurement.
The use of elbows at the front and back end of the flow meter section widens the footprint of the section. Therefore, a wide skid must be built to support the section and special permits must be obtained to transport the skid to the job site. A need exists for an ultrasonic attenuation treatment that can eliminate the use of elbows.